The present invention relates to the use of an intermittent sequence of messages to maintain synchronization between a transmitter and at least one receiver in a communication network. In particular, it relates to transmitters and receivers for use in such a network.
In a communication network comprising a plurality of transceivers it may be necessary to keep the transceivers synchronized so that they use the same timing for communicating between each other. One transceiver may act as a master defining the timing for the communication system with the others acting as slaves and keeping synchronized with the timing of the master. It may be desirable to keep power consumption of the slaves as low as possible.
One way of maintaining synchronization within the network is for the master to transmit a periodic sequence of single beacon messages, with a fixed time interval between the beacon messages. A beacon message may be a radio packet. The slaves periodically listen, every fixed time interval, for a beacon message. The periodic reception of a beacon message from the master allows the slave to compare its timing with that of the master and to adjust its timing to maintain synchronization. Furthermore, as the sequence is periodic, power consumption can be reduced if the slave receiver does not attempt to receive beacon messages in the interval between beacon messages. Consequently, the slave receivers may listen for a beacon message in a listening window of fixed duration centered at the time a beacon message is expected to be received, once every fixed time interval.
There are some problems with such a system. The system is susceptible to the loss of beacon messages. Loss may arise from interference or multipath propagation causing degradation of the beacon message such that it is not received in the listening window of the receiver. Loss may also arise if the timing of the master is varied. Such variation may be desirable when a transceiver is part of a host device such as a mobile phone which operates with a timing system which is not synchronized to the master. It may be useful to synchronize the host timing and the master timing by shifting the timing of the master so that it coincides with the host""s timing.
It would be desirable to improve the manner in which information is transmitted within a communications network.
According to the present invention there is provided a transmitter, for controlling at least one receiver by intermittently transmitting groups of messages, comprising: control means arranged to provide intermittently groups of messages for transmission, each of said groups comprising a plurality of messages in series and separated by time intervals, wherein each of the plurality of messages in a group comprises control information such that control of the receiver can be effected by the reception of any one of the plurality of messages in the group.
It should be appreciated that embodiments of the invention improve the efficiency with which messages can be transmitted without markedly increasing the power consumption of the transceivers in the network.
The control information according to the preferred embodiment is sufficient to effect synchronization between the receiver and transmitter or sufficient to effect the reactivation of the receiver from a low power mode.
In one application of the invention, a communication system comprises a transmitter according to the invention and at least one receiver for periodically receiving messages having control information. The receiver comprises control means arranged to control the operation of the receiver in dependence on received messages; a clock for providing a time reference to the control means; and receiver and synchronization means responsive, when enabled, to the control information in a received message to indicate to the control means the reception of said message, wherein said control means periodically enables for a predetermined duration said receiver and synchronization means.
For a better understanding of the present invention and to understand how the same may be carried into effect reference will now be made to the accompanying drawings in which: